mental and artistic endeavor, was
vocal music for groups of unaccompanied voices in the liturgy of the
church. About the tenth century, musicians tried the crude
experiment,[11] called Organum, of making two groups of singers move
in parallel fifths _e.g._,

[Music: Tu Patris sempiternus es Filius.]

but during the 13th and 14th centuries a method was worked out by
which the introductory tune was made to generate its own subsequent
tissue. It was found that a body of singers could announce a melody of
a certain type and that, after they had proceeded so far, a second set
of singers could repeat the opening melodic phrase--and so likewise
often a third and a fourth set--and that all the voices could be made
to blend together in a fairly harmonious whole.[12] A piece of music
of this systematic structure is called a _Round_ because the singers
take up the melody in _rotation_ and at regular rhythmic periods.[13]
The earliest specimen of a Round is the famous one "Sumer is icumen
in" circa 1225 (see Supplement of musical Examples No. 1), which shows
to what a high point of perfection--considering those early
days--musicians had brought their art. For, at any rate, by these
systematic, imitative repetitions they had secured the first requisite
of all music, coherence. This principle, once it was sanctioned by
growing musical instinct, and approved by convention, was developed
into such well-known types of polyphonic music as the Canon, the
Invention and the Fugue; terms which will be fully explained later on.
It is of more than passing interest to realize that these structural
principles of music were worked out in the same locality--Northern
France and the Netherlands, and by kindred intellects--as witnessed
the growth of Gothic architecture; and there is a fundamental affinity
between the interweavings of polyphonic or, as it is often called,
_contrapuntal_[14] music and the stone traceries in medieval
cathedrals. During the 13th and 14th centuries northern France, with
Paris as its centre, was the most cultivated part of Europe, and the
Flemish cities of Cambrai, Tournai, Louvain and Antwerp will always be
renowned in the history of art, as the birthplace of Gothic
architecture, of modern painting and of polyphonic music.[15] A great
deal of the impetus towards the systematic repetition of the voice
parts must have been caused by practical necessity (thus justifying
the old adage); for, before the days of printed music